1. Technical Field
The present disclosure relates to determining oil responsiveness and viscosity for use in control and diagnostics of an internal combustion engine and other applications having hydraulic actuators.
2. Background Art
Hydraulic actuation systems have a response that varies not only with oil pressure, but also with how fast oil pressure can change in response to a command. Fluid viscosity of the oil is a significant factor in the ability to raise or lower oil pressure. Various prior art strategies determine or estimate oil viscosity based on steady-state (or DC) oil pressure relationships that occur under specific and generally infrequent operating conditions or ranges, which delays availability of the viscosity determinations. In addition, strategies using only steady-state measurements are vulnerable to long-term drift or offset in measurement values provided by the oil pressure sensing system.
To improve control and diagnostics of hydraulic actuators, it is desirable to have a real-time strategy for robustly detecting the effective responsiveness or inferred viscosity of the oil under various system and ambient operating conditions. For internal combustion engine applications, hydraulic actuators may include a variable cam timing device, or valve deactivation system, such as used in variable displacement engines, for example.